Shirley Henderson talks about playing Claire Salter and the character's story.

What is the background to Andrew and Claire’s story?

Claire and Andrew are married and have a daughter who wants to travel the world. Andrew wants Claire to have another baby through IVF but she’s not sure. He is very happy with his life but she is subtly discontent from the start. Then this awful tragedy happens and they have to deal with the aftermath and try to move on. I think before tragedy strikes the people of Southcliffe, Claire was on the road to a breakdown and this brought it all to the surface. They both deal with it separately and very differently.

How do they deal with it separately?

Claire gradually starts to lose grip of reality and becomes increasingly troubled as everything she sees or hears becomes distorted in her mind. She had a slightly strange relationship with her daughter; it wasn’t love/hate but they certainly butted heads. She wasn’t particularly close to Anna who was more of a Daddy’s girl but as a result of the event whether through guilt or sorrow she starts to completely unravel. Meanwhile Andrew is more grounded and in tune with the best way to cope with it. However, Claire leaves Andrew feeling ostracised. She pushes him away as her own problems start to take hold.

Do you enjoy working with Eddie Marsan (who plays Claire's husband Andrew)?

He’s fantastic. I feel like we’re brother and sister on set. We have been brought up differently but we are so similar when we’re on set together. We approach things the same way and he makes me laugh and talks about things that interest me over a nice cup of tea. He’s much chattier than I ever imagined because I always had the impression he was really intense from a lot of the roles I’ve seen him in.

Have you found it hard to switch off after filming something as intense as this?

I’ve let past roles stay with me before and you have to find a way to leave it all on set otherwise you can’t sleep. I used to overwork things in my mind and would be so tired by the next morning. When you are filming you have to let it go because you have so much to do the next day, there is an anxiety that comes with this kind of work.

How did you work up to those emotional scenes with Eddie?

We allow each other time. You are often guided about being technically ready rather than us being emotionally ready. For the big stuff you never know it’s going to be big, the scene that happens by the marshes, we didn’t know how big it was going to be until it happened. Some things you just can’t plan for, you just have to be brave and let it go.